The present invention relate to an ink-jet printing method and apparatus for printing an image on a printing medium by discharging an ink from a printhead onto the medium, and a printing system including the printing apparatus.
A printer apparatus such as a printer, a copying machine, or a facsimile machine is designed to print an image consisting of dot patterns on a printing medium such as a paper sheet or a thin plastic film on the basis of image information. The print schemes for such printer apparatuses can be classified into an ink-jet scheme, a wire dot scheme, a thermal scheme, a laser beam scheme, and the like. Of these schemes, the ink-jet scheme (ink-jet printer apparatus) is designed to discharge/spray an ink (printing material) from the orifices of the printhead and cause the ink to adhere to a printing medium, thereby printing an image.
With the widespread use of printer apparatuses, demands have recently arisen for printer apparatus which can realize high-speed print operations, high resolution, high image quality, low noise, and the like. As a printer apparatus which can meet such demands, an ink-jet printer apparatus is available. The ink-jet printer apparatus is designed to print an image by discharging an ink from the printhead, and hence can perform a non-contact print operation. This printer apparatus can therefore obtain a very stable image.
With the recent developments in various types of digital cameras, digital videos, CD-ROMs, and the like, pictorial image data can be easily processed on applications in host computers. Consequently, printer apparatuses as output devices are required to have a function of outputting pictorial images. Conventionally, such pictorial image output operations are performed by high-end silver salt type printer apparatuses designed to print images upon reception of digital image data and expensive sublimation type printer apparatuses whose application is limited to photographic outputs using sublimable dyes.
In the above prior art, a printer apparatus exclusively used for prints of photographic images and the like is very expensive. This is because such a printer apparatus uses the silver salt scheme which requires a complicated process, and is too large to be used as a desktop type apparatus. Consider a printer apparatus designed to use sublimable dyes. As is known, in this case as well, as the size of a printing medium increases, the manufacturing cost of the main body and the running cost considerably increase. That is, such printer apparatuses cannot be easily used in homes. The most critical drawback of these printer apparatuses is that they are designed to use special printing media. That is, the applications of the printer apparatus are limited. For this reason, it is totally impossible for one printer apparatus to allow the user to selectively perform print operations using various types of printing media as in home and business use, e.g., printing images based on data from a wordprocessor or graphic data using plain paper in the normal mode and printing photographic images and the like using special printing media in the pictorial print mode.
According to improved printer apparatuses, especially ink-jet printer apparatuses, in order to solve these problems, image processing, coloring materials, printing media, and the like have been improved. Recently, therefore, great improvements have been made in the image quality of photographic images printed by ink-jet printer apparatuses.
In addition, as is known, a printer apparatus is becoming popular, which serves both as a monochrome printer apparatus and a color printer apparatus upon replacement of an ink cartridge integrally constituted by a printhead and an ink tank. Such a printer apparatus has been developed to enhance the monochrome print function of printing out images based on data from a wordprocessor at a high speed, and realize a function of printing color graphic images by using the limited resources of one printer apparatus. Most users are demanding this technique. This printer apparatus has a function of recognizing the type of ink cartridge and optimizing a print operation by, e.g., switching control for a monochrome cartridge and control for a color cartridge. At present, replacement of an ink cartridge is performed to only exchange a color ink and a monochrome ink.
Various studies have been made to improve the gradation characteristics of color graphic outputs in color print operations. For example, the resolution for such a print operation is set to be higher than that in the color print mode to improve the printing performance. The resolution of a printer apparatus is increased, and multivalued data is sent as print data to the printer apparatus. The printer apparatus then performs a multivalued output operation using sub-pixels. Such improvements have been proposed and put into practice.
In addition, a method of printing an image on a printing medium by using coloring materials having different pigment densities at once has been proposed to allow an ink-jet printer apparatus to print out a pictorial image. A printer apparatus designed to print an image by preparing two types of coloring materials having different pigment densities for each of coloring materials of C, M, Y, and K or C, M, and Y, and using them at once, unlike a general printer apparatus which uses four or three coloring materials of C, M, Y, and K or C, M, and Y, has been proposed. According to this printing scheme, the color reproduction range can be greatly broadened, and the graininess of an image can be made greatly reduced by printing a high-lightness area (in which printed dots are discretely present on a printing medium) of the image by using a coloring material having a low pigment density. In contrast to this, a low-lightness, high-saturation area is printed by using a coloring material having a high pigment density, which reduces the graininess of the resultant image, thereby obtaining an image with good color development.
In the above method, however, many types of coloring materials must be contained in one printer apparatus. The printer apparatus therefore becomes a very complicated system. In general, users print monochrome images in most cases. For this reason, it is often useless to always have coloring materials having low pigment densities in the printer apparatus at the same time. Furthermore, since the size of the printhead is limited, the maximum capacity for a print operation or the capacity of an ink tank for each coloring material must be reduced, thus posing problems.
The pigment density of a coloring material such as an ink is determined by the maximum necessary density in the system to be designed. The pigment density is determined to obtain a necessary optical reflection density from the maximum ejection amount in the system. In general, if the maximum saturation of a primary color (CMYK) is obtained by an ink injection amount of 100%, almost the maximum saturation of a secondary color (RGB), which is the sum of primary colors at 100%, can also be obtained. In order to broaden the color reproduction range, therefore, the pigment density of a coloring material must be increased to further increase the density of the coloring material so as to obtain the maximum saturation of a primary color with an ink ejection amount of 100%. For this reason, the graininess of a pictorial image becomes conspicuous. That is, this method is not suited for business use of graphic images.
According to another method, the maximum ejection amounts of primary and secondary color inks can be set to 200% and 400%, respectively, by decreasing the pigment densities. In a general ink-jet printer apparatus, however, since the maximum amount of coloring material which can be received is determined by the type of printing medium, the types of printing media which can be used are limited. For this reason, the versatility of the ink-jet printer apparatus deteriorates, and the running cost is high.
As described above, when a print operation is to be performed by using a thin ink, a relatively large amount of ink must be ejected onto a printing medium. In practice, the graininess of dots of thick ink, e.g., black, cyan, or blue inks, can be effectively and greatly reduced by setting the density of such an ink to about 1/3 or less that of a conventional ink. According to a simple calculation, in this case, in order to obtain an image having almost the same color density as that of an image printed by using a conventional thick ink, the thin ink must be ejected onto a printing medium in an amount about three times that of the conventional ink.
In general, if the amount of ink injected onto a printing medium per unit time exceeds the ink receiving capacity of the printing medium, or the amount (ink ejecting rate) of ink ejected onto a printing medium per unit time exceeds the ink absorbing rate of the printing medium, the ejected ink overflows the printing medium, resulting in a blurred image. Alternatively, the ink moves on the printing medium because of the surface tension. As a result, the printed image has high- and low-density portions, and hence the image quality deteriorates.
When a print operation is to be performed by using a thin ink, in particular, a large amount of ink must be ejected onto a printing medium to increase the density of an image. The above problem therefore tends to arise.
In order to meet the needs of the users, the print speed of the printer apparatus must be increased beyond a predetermined speed. For this purpose, the moving speed of the carriage or the driving speed of the head must be increased. Accordingly, the ink ejecting rate increases. As a result, problems such as an ink overflow arise more easily.